Transfer of molten magnesium along ferrous metal surface without halide flux creepage



United States Patent 3,300,298 TRANSFER OF MOLTEN MAGNESIUM ALONGFERROUS METAL SURFACE WITHOUT HA- LIDE FLUX CREEPAGE John N. Reeling,Jr., Midland, Mich., assignor to The Dow Chemical Company, Midland,Mich., a corporation of Delaware No Drawing. Filed Jan. 9, 1963, Ser.No. 250,212

' 8 Claims. (Cl. 75-67) This invention relates to wetting of metalsurfaces and more particularly concerns a method of rendering ferrousmetal surfaces 'wettable by molten magnesium.

Ordinary nominally clean ferrous metal surfaces when placed in contactwith molten magnesium are not wetted by the molten metal, that is,substanially no adhesion occurs between the magnesium and the ferroussurface. Further. when such as ferrous surface is in contact with bothmolten magnesium and molten flux it is preferentially wetted by thelatter; a thin layer of the flux will, in a remarkably short time, creepalong the entire ferrous surface completely covering it or that portionwhich is at a temperature above the melting point of the magnesium.Thus, if ferrous metal melt transferring devices such as, for example,dipping ladles, pumps and pipe lines, or open troughs are used totransfer molten magnesium, from a flux protected body thereof, and ifthe surfaces of said devices are only nominally clean, the surfaceswhich are in contact with the magnesium will become covered with flux,some of which will separate therefrom to contaminate the moltenmagnesium being transferred.

On the other hand, a clean oxide-free ferrous surface is preferentiallywetted, either in or out of the presence of flux, by molten magnesium.However, even where the ferrous surface is initially clean, it oxidizesfairly rapidly when exposed to the atmosphere, and further, the heat ofthe molten magnesium body and preheating of the transfer deviceappreciably increases the rate of oxidation making it heretoforepractically impossible to retain an oxide-free ferrous surfaceimmediately preceding immersion of the ferrous article in the bath orthe bringing together of the molten magnesium and the ferrous metal.

Reference throughout this specification to the term magnesium meansmagnesium in all commercial grades and the alloys thereof containing 50percent or more magnesium. The term nominally clean as used hereinrefers to ferrous metal surfaces which are free from gross foreignmatter such as mill scale, grease, oil and dirt but covered at leastpartially with an oxide, hydroxide, or other ferrous product of reactionwith air (and other surrounding media). Also, reference to flux is tofusible halide salt mixtures commonly used in the operations of meltingand refining magnesium.

An object of the invention is to provide a method of transferring moltenmagnesium free of flux contamination through creepage from a supply ofsaid metal which is in contact with the flux.

Other objects and advantages of the invention will become apparent fromthe detailed description presented hereinafter.

In practicing the method of this invention, the ferrous metal deviceWhich is intended to be used and whose surfaces, or a portion thereof,have been previously cleaned and adherently coated, such as, forexample, by galvanizing or electroplating with a metal which is readilysoluble in molten magnesium, for example, cadmium, copper, nickel, tin,or zinc is contacted with molten magnesium for a sufiiciently longduration to allow dissolution of the said coating metal so that3,300,298 Patented Jan. 24, 1967 the underlying clean oxide-free'ferrous surface is thereby exposed directly to the molten magnesiumbefore the intervention of air, flux, or other contaminants. Dissolutionof the coating metal'usually takes place within from about 5 to about 20minutes after immersion. Initial wetting by magnesium of the coatingmetal is thereby accomplished, with continued preferential wetting onthe exposed ferrous metal surface after dissolution of the coatingmetal. Since both the initial coated surface and the subsequentlyexposed ferrous surface are preferentially wetted by the moltenmagnesium, flux contamination through creepage along the interfacebetween the molten magnesium and the adjacent ferrous metal surface iscompletely eliminated. When the ferrous metal device is removed from themolten magnesium, a wetting film of molten magnesium remains on theferrous surface. On cooling, the magnesium film solidifies on thesurface thereof providing a wettable and protective surface over theferrous metal for subsequent use as in repeated exposure in moltenmagnesium.

It is understood that in certain cases, depending on the nature of theoperation, such as, for example, transferring molten magnesium from amelting pot wherein the magnesium is covered with molten flux, using forexample, a ferrous metal pipe to affect the transfer, not all of theferrous metal surface which is intended to contact molten magnesium needbe initially coated with one of the aforesaid metals in order to stopflux creepage along the ferrous surface at the interface between it andthe molten magnesium; but rather, only a portion of such surface overwhich the molten magnesium may pass need be coated; for example, aportion as a band from about 3 inches to about 3 feet wide, said coatedportion being located at a point between the supply reservoir containingmolten magnesium and molten flux and the destination of the moltenmagnesium. The socoated portion provides a preferentially wettablesurface by molten magnesium, with continued preferential wetting on theresulting clean exposed underlying ferrous surface after dissolution ofthe coating by the molten magnesium to form an interface of moltenmagnesium and the ferrous surface. Both the initial and final interfaceportion thus provided effectively act as a barrier to flux creepage dueto preferential wetting thereon by magnesium rather than flux, therebyeliminating flux contamination in the molten magnesium beingtransferred.

Any ferrous metal device can be treated to accomplish preferentialwetting by initially coating the suitably cleaned surface, or a selectedportion thereof, with either cadmium, copper, nickel, tin, or zinc usinga method such as, for example, galvanizing or electrodeposition wherebyall or substantially all the iron oxides and other foreign materialnormally present on ferrous metal surfaces will be removed from saidsurfaces either before or during the coating operation such that nointermediate layer of oxide or other foreign material exists between thecoating metal and ferrous metal in a quantity sufficient to preventadherence of the coating metal. Of the coating metals set forth, zinc isto be preferred.

Preferential wetting by magnesium of zinc-coated surfaces, for example,rather than nominallyclean ferrous surfaces can be clearly illustratedby immersing two pieces of steel pipe, one having been galvanized, theother uncoated, but nominally clean, into a molten magnesium bathcovered with a layer of flux. Upon withdrawing the two pieces, visualexamination shows the galvanized piece to be covered with a film ofmagnesium, whereas the uncoated piece is covered with a layer of flux. Aclose study of the microstructure of the galvanized piece after animmersion of several minutes revealed no significant trace of zinc norany flux.

The followin example further illustrates the application of the presentinvention.

Example A steel pipe galvanized both inside and out was, in conjunctionwith a pump, used to transfer molten magnesium from a melting pot inwhich the molten ma gnesiurn was covered with molten flux. The input endof the pipe when introduced into the metal was preferentially wetted bythe molten magnesium and the magnesium transferred therethrough from themelting pot was found to be free of flux. Upon subsequent sectioning andeX- ami-nation of said so used pipe it was found to be free of fluxillustrating that flux did not creep along any surfaces wetted by themagnesium.

In addition, an adherent, solidified wettable coating of magnesium wasformed on both the inside and outside surface of the pipe which was incontact with the molten magnesium.

I claim:

1. A method of preventing halide flux creepage along the interfacebetween a ferrous metal surface and molten magnesium maintained underthe protection of a molten halide flux which comprises, adherentlycoating :1 portion of said ferrous metal surface with a metal selectedfrom a group consisting of cadmium, copper, nickel, tin and zinc,contacting the said molten magnesium with the so-coated portion of theferrous metal surface, continuing said contact for a sufficient durationto dissolve the metallic coating on the so-coated portion therebyallowing the molten magnesium to make direct contact with the cleanferrous metal thereby establishing an interface along which the passageof flux is thereby prevented.

2. The method of claim 1 wherein the minimum distance across the coatedportion of the ferrous metal surface is from 3 inches to about 3 feet.

3. A method of transferring molten magnesium from a halide fluxprotected body thereof contained in ferrous metal equipment without fluxcontamination through creepage along a ferrous metal surface of amelt-transferring device at the interface between it and the moltenmagnesium which comprises, contacting the molten magnesium of the fluxprotected body with the ferrous metal melt-transferring device, aportion of Whose surface, which is intended to form an interface withthe molten magnesium having been initially adherently coated with acoating metal selected from the group consisting of cadmium, copper,nickel, tin and zinc, said coated portion being located between thesupply of molten magnesium and the destination thereof so that all themagnesium passing from the flux protected body to the destination musttraverse the coated portion, and continuing the contact of the moltenmagnesium with the said portion for a sufiicient duration to dissolvethe adherent coating by moving the molten magnesium past the saidportion toward its destination thereby allowing direct contact of moltenmagnesium with clean ferrous metal thereby exposed to the magnesium asthe molten magnesium dissolves the coating metal, the direct contact soobtained preventing flux creepage and resulting contamination in themolten magnesium transferred.

4. The method of claim 3 wherein the ferrous metal melt-transferringdevice is a pipe.

5. The method of claim 4 wherein, the length of the coated portion ofthe ferrous metal pipe is from about 3 inches to about 3 feet.

6. The method of claim 3 wherein said portion of the ferrous metalmelt-transferring device is initially coated with zinc.

7. The method of claim 3 wherein said portion of the ferrous metalmelt-transferring devioe is initially coated with cadmium.

8. The method of claim 3 wherein said portion of the ferrous metalmelt-transferring device is initially coated with tin.

References Cited by the Examiner UNITED STATES PATENTS 1,165,920 12/1915Uyeno 11751 2,550,709 5/1951 Moe et al. 11752 2,912,346 11/1959 Kanter1l751 2,935,421 5/1960 Chisholm 11752 ALFRED L. LEAVITT, PrimaryExaimner.

JOSEPH B. SPENCER, RICHARD D. NEVIUS, I. R,

BATTEN, JR., Assistant Examiners.

3. A METHOD OF TRANSFERRING MOLTEN MAGNESIUM FROM A HALIDE FLUXPROTECTED BODY THEREOF CONTAINED IN FERROUS METAL EQUIPMENT WITHOUT FLUXCONTAMINATION THROUGH CREEPAGE ALONG A FERROUS METAL SURFACE OF AMELT-TRANSFERRING DEVICE AT THE INTERFACE BETWEEN IT AND THE MOLTENMAGNESIM WHICH COMPRISES, CONTACTING THE MOLTEN MAGNESIUM OF THE FLUXPROTECTED BODY WITH THE FERROUS METAL MELT-TRANSFERRING DEVICE, APORTION OF WHOSE SURFACE, WHICH IS INTENDED TO FORM AN INTERFACE WITHTHE MOLTEN MAGNESIUM HAVING BEEN INITIALLY ADHERENTLY COATED WITH ACOATING METAL SELECTED FROM THE GROUP CONSISTING OF CADMIUM, COPPER,NICKEL, TIN AND ZINC, SAID COATED PORTION BEING LOCATED BETWEEN THESUPPLY OF MOLTEN MAGNESIUM AND THE DESTINATION THEREOF SO THAT ALL THEMAGNESIUM PASSING FROM THE FLUX PROTECTED BODY TO THE DESTINATION MUSTTRAVERSE THE COATED PORTION, AND CONTINUING THE CONTACT OF THE MOLTENMAGNESIUM WITH THE SAID PORTION FOR A SUFFICIENT DURATION TO DISSOLVETHE ADHERENT COATING BY MOVING THE MOLTEN MAGNESIUM PAST THE SAIDPORTION TOWARD ITS DESTINATION THEREBY ALLOWING DIRECT CONTACT OF MOLTENMAGNESIUM WITH CLEAN FERROUS METAL THEREBY EXPOSED TO THE MAGNESIUM ASTHE MOLTEN MAGNESIUM DISSOLVES THE COATING METAL, THE DIRECT CONTACT SOOBTAINED PREVENTING FLUX CREEPAGE AND RESULTING CONTAMINATION IN THEMOLTEN MAGNESIUM TRANSFERRED.